Thistles in warmer environments fear no weevil
written by Emma van der Heide and edited by Coleman Earnest
Summary
Biological control, a management strategy in which one species is used to suppress the population of another species, often relies on synchronized periods of activity (phenology) between the biological control agent and its target host. However, climate change can alter the seasonal timing of events within an organisms’ life cycle, leading to temporal mismatches between invasive species and their biological control agents. For invasive species managed with biological control agents, it is therefore crucial to understand how climate change affects the activity of biological control agents and their ability to prey on their target host.
In this paper, the authors studied the invasive thistle Carduus nutans (musk thistle) and its biological control agent, the weevil Rhinocyllus conicus, whose larvae feed on the thistle’s developing flower heads. They monitored populations of musk thistle along an urban-rural heat gradient in central Pennsylvania to examine a) whether flowering timing and weevil activity still matched at warmer sites; and b) whether differences in temperature lead to differences in the damage caused by the weevils. They found that temperature had no effect on the number of weevils present or the timing at which they were present relative to the thistles’ flowering stage. However, despite synchronized flowering and weevil activity at both warmer and cooler sites, thistles at warmer sites had both fewer egg cases and fewer cysts present, suggesting that rising temperatures under climate change could make R. conicus less effective against C. nutans.
Take Home Points
Phenological matching between the invasive thistle Carduus nutans and its biocontrol agent Rhinocyllus conicus did not change along an urban-rural heat gradient.
However, fewer flower heads were damaged by R. conicus at warmer sites, indicating that even when warming temperatures may not appear to impact individual organisms, interactions between organisms may change with temperature.
Management Implications
The presence of a biological control agent on its target weed does not necessarily indicate that the agent is working as expected.
R. conicus may damage fewer C. nutans flower heads under warmer conditions, necessitating the addition of other management strategies, such as mowing or herbicide, to an integrated weed management plan.
Consistent with prior studies, C. nutans flowered up to 10.6 days earlier at warmer sites, strengthening evidence that managers will need to act earlier to control this weed as the climate warms.
Related Papers
Research to Practice Papers on:
Changes to phenology changing management timelines (with C. nutans as an example)
Research Summaries: Keller & Shea, 2021; Zhang et al. 2012; Sun et al 2020
Keywords
Shifting seasons (phenology), Biological Control, Carduus nutans, Rhinocyllus conicus